In the wake of mass murders in Colorado and Wisconsin, a California lawmaker is pushing to close a "loophole" allowing owners of military-style guns to sidestep the state's assault weapons ban.

Sen. Leland Yee is gaining support from top Democrats in a bid to ban devices that allow magazines of ammunition to be reloaded so quickly that semiautomatic guns can be fired almost like assault weapons.

California already has one of the nation's toughest assault weapons bans. Permitting devices that allow dozens of bullets to be shot in a matter of seconds undermines that law, the San Francisco Democrat contends.

"That's not the kind of weapon you want hanging around in a theater, a shopping center or a school," Yee said.

Yee's effort has gained support from state Attorney General Kamala Harris and Senate President Pro Tem Darrell Steinberg, among others.

Sam Paredes, executive director of Gun Owners of California, said he believes California would be the first to ban the devices, which he said have not sent crime soaring. Such weapons can be used for recreational shooting, hunting, or for protecting your home or family members, Paredes said.

Yee's SB 249 comes in the wake of multi-victim, high-profile shootings at a Colorado movie theater in July and at a Sikh temple in Wisconsin on Sunday.

"There have been a number of incidents where some kind of automatic weapon has come into play and destroyed lives," Yee said. "There seems to be growing support for closing the (assault weapons) loophole."

Paredes countered that the two mass murders have generated "knee-jerk reactions from the typical suspects who look for opportunities to spread their anti-gun agenda."

Paredes said that gun-control advocates never mention incidents in which possessing a weapon thwarted a crime – such as when a 71-year-old Florida man scared off two would-be robbers by firing his gun at an Internet cafe in July.

California's existing assault weapons law permits the possession of certain military-style weapons if a tool is required to detach their magazine. The intent in permitting such guns was that their firepower would be limited if a tool were required to reload them, according to a fact sheet for SB 249.

But manufacturers have created devices, called "bullet buttons," that allow magazines to be detached instantly by using the tip of a bullet. A "mag magnet" can be added to allow detachment by the press of a finger, Yee contends.

"These rifles are not about marksmanship, these rifles are about killing as many individuals as possible," Yee said.

Many Republicans oppose Yee's bill.

"Criminals are going to get guns anyway," said Assemblyman Curt Hagman, R-Chino Hills. "What we're doing (with SB 249) is putting more and more burdens on law-abiding citizens."

Added Assemblyman Steve Knight, R-Palmdale, "It's just another attack on the gun industry."

Steinberg, D-Sacramento, has signed on as a co-author of SB 249. Lawmakers "can't be afraid to do what is just plain common sense," he said.

"I know that everyone is afraid of the strong lobby on the other side, and I believe in the Second Amendment," Steinberg said.

"But no one will convince me it's anything other than a joke to say that having multiple clips and semiautomatic weapons that can shoot 100 or more bullets at a time is necessary in this state or in this country," he said. "It's ridiculous."

SB 249 faces stiff opposition from pro-gun interests. The National Rifle Association says it would render hundreds of thousands of firearms sold legally in the state illegal as of next year.

The group called the bill the "worst gun confiscation threat in 20 years" in a release urging members to call lawmakers and voice opposition to the proposal.

But Amanda Wilcox, a spokeswoman for California chapters of the Brady Campaign to Prevent Gun Violence, applauded SB 249.

"Guns in the wrong hands are a threat to society, and assault weapons in the wrong hands are even worse," she said.

SB 249 is scheduled to be heard by the Assembly Appropriations next week. It must clear both houses in the next four weeks to make it to Gov. Jerry Brown's desk by the end of the session.